The objective of this research is to understand the relationship between x-ray image quality and film reader performance. The pulmonary nodule which is frequently a manifestation of primary or metastatic lung cancer and which is frequently overlooked on chest films will be used as a model system. The relationship between a physical measure that we call conspicuity which is a direct function of nodule size, contrast and edge gradient and an inverse function of background complexity and observer performance will be studied in simulated nodules and in renal pulmonary nodules collected in a clinical study. The clinical study will compare both detectability using ROC analysis and conspicuity in films made on the same patients at low and high kVp. The relative value of low vs. high kVp for chest radiography will, therefore, be quantitatively determined for lung modules.